Recombination is important in the repair of broken DNA molecules, the generation of genetic diversity, and the correct segregation of chromosomes during formation of gametes. The goal of this study is to understand the mechanisms of meiotic recombination in the yeast Saccharomyces cerevisiae. Most of the proposed experiments are focused on the analysis of a chromosomal region with a very high level for meiotic recombination (recombination hotspot). This hotspot is located upstream of the HIS4 gene. Previous studies showed that the HIS4 hotspot has a high level of meiosis-specific double-strand DNA breaks (DSBs) and the activity of the hotspot requires the binding of several transcription factors. The first specific aim is to investigate the formation and processing of recombination intermediates at the HIS4 locus. The second aim is to examine the relationship between chromatin structure and meiotic recombination. The effect of yeast mutants that "loosen" chromatin structure on hotspot activity will be studied. Long tracks of the repetitive DNA sequences of the form CCGNN (A nucleosome-excluding sequence) repress meiotic recombination, whereas shorter tracts of the same sequence elevate meiotic recombination. The third specific aim is to elucidate the mechanism by which nucleosome-excluding DNA sequences affect meiotic exchange. The fourth specific aim is to use the DNA microarray technology to map all of the strongest recombination hotspots in the yeast genome. The final specific aim is to identify the gene functions required to repair single stranded DNA loops; such loops can occur during meiotic recombination as a consequence of heteroduplex formation at a genetic locus heterozygous for an insertion or deletion.